According to one of Dark's sources, an upcoming episode features (avert your eyes, spoiler-free folks!) Aaron and Ji Yeon on the island twenty years from now.
This means they are doing some flash-forwards; the storytelling is taking a futuristic bend.
That casting notice that went out a few weeks ago? It could be...
Here's the thing.
It's so specific. Two to four years old, Caucasian, girl, brown hair, brown eyes.
Why so specific? Seriously, please tell me any reasons why the show would be specific about eye color. I just did a scroll through Dark's "casting" tag, and only found one other notice--out of probably about two dozen--that specified eye color. And that one didn't specify hair color. Basically, this has the most appearance specificity of any notice that's gone out for all of season five so far.
Now, Desmond and Penny both have brown eyes, but they also both have sandier colored hair. Which is not to say that this little girl couldn't be Desmond and Penny's OTProgeny, it's just that I don't really understand why they'd be so specific about her hair color, if that was the case.
She could also be, as some people in the comments over at Dark have suggested, Little Kate. Except this doesn't seem very likely for a couple of reasons. #1: We seem to be kind of done with traditional flashbacks. We are going to see Little Sayid, though, so that's a kick in the face for my logic there. #2: I would normally expect an episode involving Little Kate to involve lots of Little Kates, in the style of "Cabin Fever." There were no similar notices.
She could be a lot of things.
My brain is working overtime to try and figure it out. Because half of my brain is saying "She could be ANYONE" and the other half is saying "Who else could she POSSIBLY be?"
I'm still not ready to say it out loud, and if this kid turns out to be Baby Widmore-Hume or Little Kate or Child #4, I'll deny ever having thought the things I'm thinking. Because I'm not thinking them.